<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <!-- height,width,border属性只作为展示，样式在CSS定义 -->
    <img 
        src="images/up.png" 
        alt="一个向上的箭头" 
        title="返回顶部" 
        height="50px" 
        width="50px" 
        border="1px">
</body>
</html>